Environmental influences that support less healthful food choices and sedentary behaviors have contributed to the epidemic increase in overweight and obesity among US adults. Worksite settings are an effective channel through which to reach adults with interventions designed to prevent excess weight gain and obesity. Bus drivers are a workforce sector at high risk for excess weight gain and obesity. However, no previous studies have targeted this group for prevention interventions around weight gain and obesity. The proposed study will evaluate the efficacy of a two-year, multi-component environmental intervention to prevent excess weight gain among 1200 bus drivers working in four garages in a major metropolitan area. Four garages will be randomized to the intervention or control group for a two-year period. The environmental interventions are based on a social ecological framework and target four worksite environmental areas: 1) food availability and incentives (e.g., healthy foods in garage vending machines); 2) physical activity opportunities and incentives (e.g., attractive garage exercise facilities); 3) the social environment (e.g., group competitions for weight loss, physical activity); 4) media/promotion related to healthy food choices, physical activity and body weight (e.g., nutrition information labels on vending machine food and beverages). In addition to the environmental intervention components, social cognitive theory is used to develop interventions for individual-level behavior change. Body weight, energy intake and physical activity behavior will be measured at baseline and every six months for a two-year period, with a six-month post-intervention measurement. It is hypothesized that during the two-year intervention period, compared to drivers in the control garages, drivers in the intervention garages will gain less weight, report lower energy intake and higher physical activity levels. The effect of the intervention on health claims costs, work absenteeism and worker's compensation claims will be evaluated as a secondary outcome.